Optical glass and optical element

ABSTRACT

The present invention is aimed to provide a cost-effective optical glass with refractive index of 1.74-1.80 and Abbe number of 47-51 but containing no Gd 2 O 3  and an optical element made hereof. The optical glass contains the following components according to percentage by weight: more than 2.7% but less than 10% of SiO 2 , 20-31% of B 2 O 3 , 38-49% of La 2 O 3 , more than 12% but less than 20% of Y 2 O 3 , more than 1% but less than 4% of ZnO, more than 0.5% but less than 3% of Nb 2 O 5 , wherein the content of ZnO is more than that of Nb 2 O 5 , 0-5% of Ta 2 O 5 , 0-5% of RO, wherein the RO is one or more of CaO, SrO and MgO, and content of ZrO 2  is more than 6.7% but less than 15%. The present invention is a lanthanum borate glass containing no Gd 2 O 3 . A stable glass can be obtained by adjusting the content of La 2 O 3 , B 2 O 3  and Y 2 O 3 .

FIELD OF THE INVENTION

The present invention relates to an optical glass with refractive indexof 1.74-1.80 and an Abbe number of 47-51 and an optical element madehereof.

BACKGROUND OF THE INVENTION

In recent years, with the increasing integrated level and rapidlyincreasing functions of the equipment applied in the optical system, theoptical system is required to be more accurate, lighter and smaller. Inorder to meet the refractive index of 1.74 to 1.80 and Abbe number of 47to 51, the optical glass is often B₂O₃—La₂O series. Japanese patentapplication laid-open No. 2006-117506 discloses an optical glass withrefractive index of 1.74-1.80 and Abbe number of 47-51. However, theoptical glass contains 25-35% (by wt %, hereinafter the same) of Gd₂O₃.Gd₂O₃ is rare earth oxide and expensive so that the optical glass isfeatured in high cost.

SUMMARY OF THE INVENTION

The present invention is aimed to provide a cost-effective optical glasswith refractive index of 1.74-1.80 and Abbe number of 47-51 butcontaining no Gd₂O₃ and an optical element made hereof.

The present invention solves the technical problem by the followingtechnical solution: an optical glass containing the following componentsaccording to percentage by weight: more than 2.7% but less than 10% ofSiO₂, 20-31% of B₂O₃, 38-49% of La₂O₃, more than 12% but less than 20%of Y₂O₃, more than 1% but less than 4% of ZnO, more than 0.5% but lessthan 3% of Nb₂O₅, wherein the content of ZnO is more than that of Nb₂O₅,0-5% of Ta₂O₅, 0-5% of RO, wherein the RO is one or more of CaO, SrO andMgO, and content of ZrO₂ is more than 6.7% but less than 15%.

Further, the SiO₂: 3-9%.

Further, the SiO₂: 3-6%.

Further, the La₂O₃: 40-49%.

Further, the La₂O₃: 43-47%.

Further, the content of the Y₂O₃ is more than 12% but less than 17%.

Further, the content of the Y₂O₃ is more than 12% but less than 15%.

Further, the content of ZrO₂ is more than 6.7% but less than 12%.

Further, the content of ZrO₂ is more than 6.7% but less than 10%.

Further, the content of the ZnO is more than 1% but less than 2%.

Further, the content of the Nb₂O₅ is more than 0.5% but less than 2.5%.

Further, the optical element made of the above optical glass.

The beneficial effects of the present invention are as follows: thepresent invention is a lanthanum borate glass containing no Gd₂O₃. Astable glass can be obtained by adjusting the content of La₂O₃, B₂O₃ andY₂O₃. Introduction of proper amount of Y₂O₃ can improve thetransmittance, reduce the density, reduce the maximum crystallizationtemperature of the glass and make the glass formable; introduction ofZnO can improve the chemical stability of the glass and inhibitcrystallization; introduction of small amount of Nb₂O₅ can adjust theAbbe number of the glass; and optical glass of said optical constantsand good chemical stability can be get by adjusting the content of ZnOand Nb₂O_(5.) The optical glass of the present invention contains noGd₂O₃ so that the cost is reduced. Experimental results show that theglass of the present invention is featured in refractive index of1.74-1.80, Abbe number of 47-51, transmittance of below 370 nm,excellent transmittance and level I of resistance to acid and water sothat it can meet the imaging requirements of the optical system andequipment.

EMBODIMENTS

The following is aimed to give complete and clear description of thetechnical solutions of the embodiments of the present invention.Obviously, the described embodiments are not all but only some of theembodiments of the present invention. Based on the embodiments of thepresent invention, all other embodiments obtained by technicians in thisart without any creative effort shall belong to the protective scope ofthe present invention.

The optical glass of the present invention contains SiO₂, which canincrease the mechanical strength of the glass material and make theglass material have good abrasion resistance and chemical resistance. Incase that the content of SiO₂ is too low, the glass is unstable and isprone to crystallization. In case that the content of SiO₂ is too high,the glass will be refractory. Therefore, the amount of SiO₂ is more than2.7% but less than 10%, preferably to be 3-9% and most preferably to be3-6%.

As an effective oxide for forming glass network structure, B₂O₃ is alsoan effective ingredient for improving meltbility, reducing the meltingtemperature and reducing the viscous flow temperature of the glass.Meanwhile, it is still an essential component to realize the lowdispersivity of glass of the present invention and it can alsocontribute to dissolution of La₂O₃. Too much B₂O₃ can not realize thehigh refractive index of the glass while too less B₂O₃ will make theglass unstable. Therefore, the content of B₂O₃ is 20-31%.

La₂O₃ is an important component to obtain glass of high refractive indexand low dispersivity. Its amount is required to be 38-49%. In case thatcontent is less than 38%, the refractive index and low dispersivity isdecreased; in case that the content exceeds 49%, devitrificationresistance is decreased, resulting in that it is difficult to preparestable glass. Thus, the content is preferably 40-49% and more preferably43-47%.

Y₂O₃ is an important component for preparing glass with high refractiveindex in the present invention in case that Abbe number is reduced.Introduction of proper amount of Y₂O₃ can improve the transmittance,reduce the density, reduce the maximum crystallization temperature ofthe glass and make the glass formable. Thus, the amount of Y₂O₃ is morethan 12% but less than 20%, preferably more than 12% but less than 17%and most preferably more than 12% but less than 15%.

The present invention is a lanthanum borate glass containing no Gd₂O₃. Astable glass can be obtained by adjusting the content of La₂O₃, B₂O₃ andY₂O₃.

Addition of ZrO₂ can realize the required refractive index. Addition ofappropriate amount of ZrO₂ can not only improve impermeabilityresistance of the glass but also effectively improve thehigh-temperature viscosity and chemical stability of the glass.Therefore, the amount of ZrO₂ is more than 6.7%, or the effect can notbe achieved. However, it should be less than 15%, or the glass is proneto crystallization. The content is preferably more than 6.7% but lessthan 12%, and more preferably more than 6.7% but less than 10%.

In the present invention, ZnO is also an essential component forpreparing the glass of high refractive index and low dispersivity. Itcan not improve impermeability resistance of the glass, reduce itsviscosity flow temperature, improve chemical stability of the glass andsuppress crystallization. The addition amount should be more than 1%,otherwise the meltbility of the glass will be reduced and the chemicalstability will be deteriorated; however, the content should be less than4%, or it is unable to obtain the final product glass of lowdispersivity of the present invention. The content is preferably morethan 1% but less than 2%.

Nb₂O₅ is also an effective component to obtain glass of high refractiveindex. In the present invention, small amount of Nb₂O₅ is added in orderto adjust the Abbe number of the glass and suppress crystallization. Theaddition amount is more than 0.5% but less than 3% and preferably morethan 0.5% but less than 2.5%.

The content of the ZnO is more than that of Nb₂O₅.

Similar to Nb₂O₅, Ta₂O₅ is also a component with the effect of realizinghigh refractive index. Proper amount of Ta₂O₅ can be added to thepresent invention. Since it is expensive, the content should becontrolled to be 0-5% and preferably 0%.

Small amount of RO can be added to the present invention, wherein the ROis one or more of CaO, SrO and MgO, in order to improve the meltbilityof the glass, wherein its content is 0-5%.

No Gd₂O₃ is added to the present invention. The optical glass withrefractive index of 1.74-1.80, Abbe number of 47-51 and level I ofresistance to acid and water and other chemical stability properties canbe obtained by adjusting the content of ZnO and Nb₂O₅, wherein thecontent of ZnO is more than that of Nb₂O₅.

According to the present invention, the optical glass is preferablyprepared in the following steps:

Using oxide, hydroxide, carbonate or nitrate of the above components asraw materials, mixing and placing them into a platinum crucible to bemelt, clarified and homogenized at 1200-1400° C. and preferably1280-1350° C. to obtain molten glass; cooling the molten glass to below1100° C. and then pouring it into preheated metal mold; performingextrusion forming on the molten glass in the metal mold at 650-750° C.,and then performing anneal on the glass after extrusion forming toobtain optical glass.

Performance test is performed on the optical glass as follows:

The annealing value in case of refractive index (nd) of (−2° C./h)-(−6°C./h), refractive index and Abbe number should be tested in accordancewith the test method for refractive index and dispersion coefficient ofcolorless optical glass specified in GB/T 7962.1-1987;

Density is tested according to GB/T 7962.20-1987 Colorless Optical GlassTest Method-Density Test Method.

The glass is made into a 10 mm±0.1 mm thick sample, wherein thewavelength of the tested glass should be λ70 in case of transmissivityof 70%.

According to GB/T 17129 test method, acid resistance and waterresistance of the tested glass can be calculated.

Besides, the temperature gradient furnace method is adopted to measurethe crystallization properties of the glass. The glass is made into180*10*10 mm sample, with the side polished, and then is placed intotemperature gradient furnace for insulation for 4 hours. Then, observethe crystallization of the glass under the microscope. The maximumtemperature at which crystal appears on the glass should be the maximumcrystallization temperature.

After testing, the optical glass of the present invention has thefollowing properties:

The refractive index range is 1.74-1.80, Abbe number 47-51 density below4.24 g/cm³ and wavelength λ80 below 370 nm in case of 80% oftransmissivity; the maximum devitrification temperature is below 1100°C.; and chemical stability and resistance to acid and water is level 1.

The optical glass of the present invention is featured in highrefractive index, excellent transmission, good chemical stability andlow density. The refractive index of the optical glass of the presentinvention is 1.74-1.80 and preferably 1.76-1.79; Abbe number is 47-51and preferably 48.5-50.5; glass density is below 4.24 g/cm³, preferablybelow 4.20 g/cm³ and more preferably below 4.18 g/cm³; wavelength λ70 isbelow 370 nm and preferably below 365 nm in case of transmissivity of70%; the maximum devitrification temperature is below 1100° C. andpreferably below 1050° C.; and chemical stability, acid resistance andalkali resistance reach level 1.

The present invention also provides an optical element made of theoptical glass described in the above technical solutions in the methodfamiliar to the technicians in the art. Since the optical glass isfeatured in high refractive index and low glass transition temperature,the optical element is also featured in high refractive index and lowglass transition temperature and can be applied to digital cameras,digital video cameras, camera phones and other devices.

In order to further understand the technical solution of the presentinvention, the following describes the preferred embodiments of thepresent invention. It should be understood that the description merelyaims to further illustrate the features and advantages of the presentinvention but not to limit the claims of the present invention.

The optical glass is prepared according to the mixture ratio of rawmaterials as shown in Table 1 in the following steps:

Fully mixing the raw materials described in Table 1, and then placingthem in a platinum crucible to be melted, clarified and homogenized at1300° C. to obtain molten glass;

Cooling the molten glass to below 1100° C. and then pouring it intopreheated metal mold;

Performing extrusion forming on the molten glass in the metal mold at700° C., and then performing anneal on the glass after extrusion formingto obtain optical glass.

Performance test is performed on the optical glass and the results areshown in Table 1. Table 1 shows the performance parameters of theoptical glass of the embodiment of the present invention.

TABLE 1 Mixture ratio of raw materials for preparing the optical glassin embodiments 1 to 10 of the present invention Embodiments 1 2 3 4 5 67 8 9 10 Glass SiO₂ 2.8 4.1 6.0 5.7 3.3 5.0 3.8 4.2 3.7 3.6 CompositionB₂O₃ 31 29 29.8 30 30.1 30.5 29.8 29.1 30.7 31 (wt %) La₂O₃ 38 38.3 39.341 39 38.1 43.8 38.4 42.6 40.1 Y₂O₃ 13.7 18.6 12.4 12.4 13.5 14.3 12.413.2 13.0 12.3 ZnO 3.5 2.1 3.1 1.9 2.4 2.9 1.9 3.7 1.8 2.0 Nb₂O₅ 0.7 1.22.3 1.6 1.2 2.0 1.4 2.9 1.5 1.8 ZrO₂ 6.8 6.9 7.1 7.0 7.8 7.2 6.9 8.5 6.79.2 Ta₂O₅ 3.5 0 0 0.4 1.9 0 0 0 0 0 RO 0 0 0 0 0.8 0 0 0 0 0 CaO 0 0 0 00 0 0 0 0 0 SrO 0 0 0 0 0.8 0 0 0 0 0 MgO 0 0 0 0 0 0 0 0 0 0 Total 100100 100 100 100 100 100 100 100 100 Performance Refractive 1.7590 1.76121.7720 1.7905 1.7690 1.7723 1.7740 1.7811 1.7829 1.7689 index ParametersAbbe 48.3 48.9 49.1 49.9 48.8 49.6 49.7 48.6 47.5 50.1 number Density4.24 4.22 4.20 4.19 4.23 4.24 4.23 4.22 4.20 4.23 (g/cm³) λ80 (nm) 370369 366 368 365 370 370 369 368 370 Maximum 1100 1080 1080 1090 11001050 1100 1090 1080 1100 crystallization temperature (° C.) ResistanceLevel 1 Level 1 Level 1 Level 1 Level 1 Level 1 Level 1 Level 1 Level 1Level 1 to acid Resistance Level 1 Level 1 Level 1 Level 1 Level 1 Level1 Level 1 Level 1 Level 1 Level 1 to alkali

It can be seen from Table 1 that the optical glass of the presentinvention is featured in high refractive index, good chemical stability,low density and excellent transmission performance.

The above description of the disclosed embodiments enables theprofessional and technical personnel in this art to realize or use thepresent invention. Various modifications to these embodiments areapparent to the skilled technicians in this art. The general principlesdefined herein may be realized in other embodiments without departingfrom the spirit or scope of the present invention. Accordingly, thepresent invention will not be limited to these embodiments shown hereinand will meet the broadest range consistent with the principles andnovel features disclosed herein.

The invention claimed is:
 1. An optical glass is characterized in thatit comprises the following components according to percentage by weight:more than 2.7% but less than 10% of SiO₂, 20-31% of B₂O₃, 38-49% ofLa₂O₃, more than 12% but less than 20% of Y₂O₃, more than 1% but lessthan 4% of ZnO, more than 0.5% but less than 3% of Nb₂O₅, wherein thecontent of ZnO is more than that of Nb₂O₅, 0-5% of Ta₂O₅, 0-5% of RO,wherein the RO is one or more of CaO, SrO and MgO, and content of ZrO₂is more than 6.7% but less than 15%.
 2. The optical glass according toclaim 1 wherein the content of SiO₂ is 3-9%.
 3. The optical glassaccording to claim 1 wherein the content of SiO₂ is 3-6%.
 4. The opticalglass according to claim 1 wherein the content of La₂O₃ is 40-49%. 5.The optical glass according to claim 1, wherein the content of La₂O₃ is43-47%.
 6. The optical glass according to claim 1, wherein the contentof Y₂O₃ is more than 12% but less than 17%.
 7. The optical glassaccording to claim 1 wherein the content of Y₂O₃ is more than 12% butless than 15%.
 8. The optical glass according to claim 1 wherein thecontent of ZrO₂ is more than 6.7% but less than 12%.
 9. The opticalglass according to claim 1, wherein the content of ZrO₂ is more than6.7% but less than 10%.
 10. The optical glass according to claim 1wherein the content of ZnO is more than 1% but less than 2%.
 11. Theoptical glass according to claim 1 wherein the content of Nb₂O₅ is morethan 0.5% but less than 2.5%.
 12. An optical element made of the opticalglass according to claim 1.